The contractile function of heterogeneously perfused segments (HET) after circumflex coronary artery occlusion (CAO) was examined in conscious dogs. At 1 h after CAO, regional shortening (SH) in nonischemic segments did not change from pre-CAO base line, and regional endocardial blood flow (REBF) increased (P less than 0.05) to 1.52 +/- 0.20 from 1.06 +/- 0.08 ml.min-1.g of tissue-1. In ischemic segments, SH was replaced by paradoxical bulging, and REBF averaged 0.07 +/- 0.02 ml.min-1.g of tissue-1. In HET with one crystal of each pair in nonischemic myocardium and the other in severely ischemic myocardium, SH at 1 h after CAO was reduced (P less than 0.01) by 53.2 +/- 3.4%. REBF maps constructed with serial sections of ventricular rings containing the crystals revealed that in HET 50 +/- 5% of the myocardium was ischemic. Therefore, in the acute phase of ischemia, the reductions in SH in HET were proportional to the amount of ischemic myocardium between recording sites. In HET, SH significantly recovered (P less than 0.01) over 4 wk after CAO but remained depressed by 26.8 +/- 5.1%. In contrast, SH in ischemic segments did not improve after CAO. In HET, the effects of inotropic stimulation and changes in left ventricular afterload on SH (as percent of base line) were similar before and at 1-4 wk after CAO. Thus, in HET, the level of dysfunction is acutely determined by the amount of ischemic myocardium between recording sites. Over 4 wk after CAO, SH improved substantially in these segments, and contractile function was not adversely influenced by an inotropic stimulation or an increase in ventricular afterload.